1. Field of the Invention
The present invention relates to an antibacterial water absorbing composition having excellent water absorption performance and antibacterial performance. The invention is further directed to absorbing materials particularly for absorbing urine, blood, other body fluids and the like, and to methods of producing the water absorbing composition.
2. Description of the Related Art
Water absorbing resins are widely used in water absorbing materials or water absorbing articles such as disposable diapers, incontinence pads, sanitary napkins, nursing pads, sheets for pets, absorbent materials for pets litter, excretion treating agents, waste blood gelling materials, drip absorbers and freshness retaining materials. The devices rely on the resins for their water absorbing performance, water retention capacities, gelling properties and the like. However, although the conventional water absorbing resin has excellent absorption and retention capacities for urine, blood and other body fluids, the resins do not have antibacterial properties.
Therefore, when the water absorbing resin absorbs urine, blood, and other body fluids and the like, the organic materials contained in the fluids absorbed by the resin are degraded by various fungus and microorganisms, thereby causing, for example, bad odors, skin irritations, and skin rashes. Further, the hydrogels are easily putrefied by the fungus and the microorganisms contained in the fluids being absorbed or the bacteria in the air, and bad odors may develop due to the putrefaction. To avoid these problems and to maintain a hygienic and safe environment, materials which exhibit both absorptive properties and antibacterial properties are desired. In particular, the problems of developing bad odors or rashes are serious in the water absorbing materials such as disposable diapers for the bedridden elderly and the sick. Accordingly, a continuing need exists to solve these problems.
The prior methods for providing absorbing materials with antibacterial properties include methods of spraying a water absorbing resin with an aqueous solution of specific antibacterial component as disclosed in Japanese Kokoku No. 3-14867. Other prior methods include adding an aqueous solution of a specific antibacterial component after mixing a water absorbing resin and an inorganic material together as disclosed in Japanese Kokoku No. 4-17058. The compositions prepared by these methods are proposed for use in water absorbing materials.
Although these prior compositions exhibit some antibacterial function and water absorbing function, they are not necessarily satisfactory for water absorbing materials. For example, in the method of spraying a water absorbing resin with an aqueous solution of a specific antibacterial component, the water absorbing resin easily coagulates and forms lumps when the resin contacts the aqueous solution of the antibacterial agent. Consequently, it is difficult to uniformly mix the water absorbing resin with the solution of an antibacterial component, and it is difficult to obtain a composition with the stabilized antibacterial properties. Furthermore, the spray process requires an evaporating step to remove the excess or other solvent after mixing and grinding and adjusting the particle size of the dried material, thereby complicating the production process.
The process of adding an aqueous solution of a specific antibacterial component to mixtures of a water absorbing resin and an inorganic material also forms lumps as described above, although usually not to the same extent. However, the aqueous solution of the antibacterial component is absorbed in the water absorbing resin and also in the inorganic material, so that the distribution of the antibacterial component becomes non-uniform. This causes large variations in the antibacterial performance of the composition and the material. Further, the increased likelihood of the dust escaping creates environmental concerns. The fine dust particles of the hydrophilic resins is difficult to control and remove from the air. Accordingly, there is a continuing need in the industry for improved methods of producing water absorbing resins with antibacterial properties.
The present invention is directed to antibacterial water absorbing compositions having excellent water absorption performance and antibacterial performance. The composition of the invention is a free-flowing powder having improved powder handling properties with lower amounts of dust being produced during manufacture. The composition is particularly useful for absorbing urine, blood, body fluids, and the like, and in the manufacture of absorbing materials such as disposable diapers, absorbent pads, sanitary napkins and the like.
The present invention is an antibacterial water absorbing composition comprising a mixture of powders of a water absorbing resin and an antibacterial powder mixture. The antibacterial powder mixture is prepared by allowing fine particles of porous inorganic adsorbent powders to adsorb an aqueous fluid of an antibacterial agent. The antibacterial water absorbing composition is obtained by allowing fine particles of porous inorganic powders to absorb an aqueous fluid of an antibacterial component and then mixing the particles with a particulate water absorbing resin.
Accordingly, a primary object of the invention is to provide an antibacterial water absorbing composition that is easy and economical to manufacture.
Another object of the invention is to provide an antibacterial water absorbing composition that is effective in inhibiting bacterial and fungal growth in aqueous fluids absorbed in the composition.
A further object of the invention is to provide an antibacterial water absorbing composition containing an antibacterial agent adsorbed in an inorganic porous adsorbent powder.
Still further object of the invention is to provide a method of producing an antibacterial water absorbing composition where the composition is produced by adsorbing an aqueous solution of an antibacterial agent in an inorganic porous adsorbent powder.
The objects of the invention are basically attained by providing an antibacterial water absorbing composition comprising a mixture of:
at least one particulate water absorbing resin;
and at least one antibacterial powders comprising at least one particulate inorganic adsorbent powder having adsorbed therein at least one antibacterial agent;
wherein said composition is a substantially free-flowing powder having water absorbing properties, and wherein said antibacterial agent inhibits bacterial growth in aqueous liquids adsorbed by said composition.
The objects of the invention are further attained by providing an antibacterial water absorbing material comprising at least one water absorbing substrate; and at least one water absorbent gel-forming composition, said composition comprising a mixture of a particulate water absorbing resin and an antibacterial powder comprising a particulate inorganic adsorbent powder having adsorbed therein an antibacterial agent.
The objects of the invention are also attained by providing a process for producing an antibacterial water absorbing composition comprising the step of:
mixing a particulate inorganic adsorbent and an aqueous fluid of an antibacterial agent whereby said antibacterial agent is adsorbed by said adsorbent to form an antibacterial powder, and
mixing said antibacterial powder with a particulate water absorbing resin to produce said composition.
These and other objects, advantages and salient features of the invention will become apparent from the detailed description of the invention.
The present invention is directed to a water absorbing composition having antibacterial properties. The composition contains an effective amount of an antibacterial agent to inhibit the growth of bacterial, fungus and other microorganisms in aqueous fluids absorbed in the composition. The invention is further directed to a method of producing the antibacterial water absorbing composition.
The antibacterial water absorbing composition basically comprises a substantially dry blend of a water absorbing resin and an antibacterial agent-containing powder. The antibacterial agent-containing powder comprises a particulate inorganic carrier and an antibacterial agent adsorbed in the carrier.
The antibacterial water absorbing composition contains about 0.1% to about 10% by weight of the antibacterial powder based on the weight of said water absorbent resin.
The carrier is a substantially dry, free-flowing particulate inorganic porous adsorbent. The adsorbent contains an effective amount of a compound having antibacterial and/or antifungal activity adsorbed on the adsorbent. The antibacterial composition is prepared by mixing an inorganic adsorbent with an aqueous fluid of an antibacterial agent. The aqueous fluid is provided in an amount which can be adsorbed by the adsorbent and produce a free-flowing powder.
The inorganic carrier is generally a particulate adsorbent having a porous form. Examples of suitable particulate inorganic porous adsorbent (A) for use in the present invention include natural or synthetic zeolites, silicon dioxide, aluminum oxide, magnesium oxide, and aluminum silicate and thereof. In embodiments of the invention, two or more of the adsorbents can be used in combination. Aluminum oxide, magnesium oxide, and silicon dioxide are generally preferred. Fine particulate hydrophilic silica prepared by wet process or dry process are most preferable.
The pore diameter of the inorganic particulate is not particularly limited so long as the adsorbent powders (A) are sufficiently porous to adsorb the antibacterial agent and release the antibacterial agent when the composition absorbs moisture. Typically, the inorganic particles have a pore diameter ranging from about 1 to 500 angstroms, and preferably from about 2 to about 200 angstroms.
The particle size of the inorganic porous adsorbent powder (A) is not particularly limited. The particles have an average particle size of primary particles typically within a range of about 0.01 to about 100 microns, preferably within a range of about 0.05 to about 50 microns, and more preferably within a range of about 0.05 to about 20 microns.
The specific surface area of the inorganic porous adsorbent powder (A) is not particularly limited. Typically, the surface area of the inorganic porous adsorbent powder (A) fall within a range of about 10 to about 800 m2/g. Preferably, the inorganic porous adsorbent powder (A) have a surface area of about 20 to about 600 m2/g determined by the BET method.
Suitable examples said antibacterial agent (B) for use in the present invention include those which can suppress the proliferation of various fungus and bacterial, such as, for example, E. coli, Providencia vettgeri, Candida albicans, Staphylococcus and other microorganisms. The antibacterial agent is preferably water soluble.
Examples of suitable antibacterial agent (B) include quaternary ammonium salt compounds containing at least one aliphatic alkyl with 6 to 18 carbon atoms in its molecule, benzalkonium salt compounds, chlorohexidine compounds, polymethylenebisguanidine compounds, and mixtures thereof.
Examples of preferred quaternary ammonium salt compounds contain quaternary ammonium cation group with hydrochloride salt or organic acid salt, said cation group containing at least one aliphatic alkyl group having 6 to 18 carbon atoms. Examples of suitable quaternary ammonium groups include hexyl trimethyl ammonium, decyl trimethyl ammonium, lauryl trimethyl ammonium, myristyl trimethyl ammonium, cetyl trimethyl ammonium, stearyl trimethyl ammonium, didecyl dimethyl ammonium, dilauryl dimethyl ammonium, and distearyl dimethyl ammonium group. The anion can be from, for example, an inorganic compound such as hydrochloric acid, bromic acid, and nitric acid, and organic acid compounds such as aliphatic monocarboxylic acids having 1-30 carbon atoms, aliphatic oxycarboxylic acids, aliphatic polycarboxylic acids, and aromatic carboxylic acids.
Examples of benzalkonium compounds include benzalkonium chloride, benzalkonium gluconate, and benzalkonium adipate. The chlorohexidine compounds including, for example, chlorohexidine, chlorohexidine hydrochloride, and chlorohexidine gluconate. Examples of polymethylene biguanidine compounds include, hydrochlorides or gluconates of polyhexamethylene guanidine, and hydrochlorides or gluconates of polyoctamethylene guanidine.
The amount of the antibacterial agent (B) incorporated into the inorganic porous adsorbent powder (A) can vary depending on the effectiveness of the agent and the intended use of the resulting composition. The inorganic porous adsorbent powder (A) generally contains about 0.5% to about 40% by weight, and preferably about 1.0 to about 30% by weight of the antibacterial agent (B) based on the solid weight of the antibacterial powder (C). Thus, the ratio of the weight of the inorganic porous adsrobent powder (A) particles to the weight of the antibacterial agent (B) is about 60:40 to about 99. 5:0.5, and preferably about 70:30 to about 99:1.
The inorganic porous adsorbent powder (A) preferably includes at least 0.5% by weight of the antibacterial agent (B), since below this level the antibacterial activity is generally unacceptably low. To obtain the satisfactory antibacterial effect at lower % by weight of antibacterial agent, it is necessary to use a large volume of the antibacterial powder (C), which typically reduces the absorption performance of the resulting composition.
When the antibacterial powder (C) contains more than 40% by weight of the antibacterial agent (B), the adsorbency of the inorganic porous adsorbent powder (A) is insufficient, thereby deteriorating the powder flow properties. Furthermore, high amounts of the antibacterial agent require an additional drying process to improve the powder flow properties, thereby increasing the manufacturing costs.
The antibacterial agent (B) is preferably prepared as an aqueous fluid, such as an aqueous solution, dispersion or emulsion more preferably aqueous solution. The aqueous fluid is then mixed with the inorganic porous adsorbent powder (A). The aqueous fluid is adsorbed by the inorganic particulate adsorbent to form a free-flowing powder or pulverulent material. The resulting powder can be dried as necessary to remove excess moisture. The amount of the aqueous fluid of the antibacterial agent (B) mixed with the inorganic particulate adsorbent (A) will vary depending on the selection of adsorbent (A), the concentration of fluid of agent (B) and the expected use of the final product. The antibacterial agent (B) typically is mixed with about 0.7% to about 70% by weight, and preferably about 1.0% to 60% by weight of the aqueous fluid based on the combined weight of the inorganic adsorbent (A) and aqueous fluid. The resulting mixture has an adsorbent (A) to aqueous fluid ratio of about 30:70 to about 99.3:0.7, and preferably about 40:60 to about 99:1.
When the inorganic adsorbent contains less than about 0.7% of the aqueous fluid of the antibacterial agent (B), the concentration of the antibacterial agent (B) in the aqueous fluid is required to be so high that it is difficult to homogeneously disperse the antibacterial agent in the aqueous fluid. Mixing the inorganic adsorbent (A) with more than 70% by weight of the aqueous fluid produces a powder with poor flow properties. Additionally drying and grinding steps are then required in order to improve the powder flow properties, which increase the cost of manufacture.
The average particle size of the antibacterial powder (C) ranges from about 0.1 to about 100 microns, and preferably ranges from about 0.5 to about 50 microns. An average particle size less than 0.1 microns results in an increase of dusting during handling. An average particle size greater than about 100 microns is difficult to mix homogeneously with the water absorbing resin (D).
The antibacterial water absorbing composition of the present invention can be prepared using standard industrial apparatus capable of mixing the inorganic particulate adsorbent (A) and the aqueous fluid of the antibacterial agent (B) to allow the adsorbent (A) to absorb the aqueous fluid.
Examples of suitable apparatus include a V-shaped rotating mixer, a Nauta blender, a ribbon blender, a planetary mixer, a conical blender, a turbulizer, an universal mixer, a kneader, and a screw mixer as known in the art.
The antibacterial powder (C) can be prepared by adding the adsorbent (A) to a mixer and adding an aqueous fluid of an antibacterial agent (B) in incremental amounts to uniformly disperse the materials. Typically, the aqueous fluid is added by spraying at a controlled rate while operating the mixer. In further embodiments, the aqueous fluid can be added in a batch process.
The inorganic adsorbent (A) and the aqueous fluid of the antibacterial agent (B) can be mixed at room temperature or at elevated temperatures. Typically, the components are mixed for about 10 to 60 minutes or until thoroughly mixed and the aqueous fluid is adsorbed.
The water absorbing resin (D) is preferably a water absorbing resin containing a carboxyl or carboxylate group (salt of carboxyl group) as the constituent unit. The resin can be produced according to known processes for producing water absorbing resins.
Examples of preferred water absorbing resin (D) for use in the present invention include:
crosslinked copolymers of starch-acrylic acid or acrylates as disclosed in Japanese Kokoku Nos. 53-46199, 53-46200;
self-crosslinked polyacrylates and salts thereof or crosslinked polyacrylates and salts thereof obtained by reversed-phase suspension polymerization, as disclosed in Japanese Kokoku No. 54-30710 and Kokai No. 56-26909;
crosslinked polyacrylic acids and salts thereof obtained by aqueous solution polymerization such as, for example, adiabatic polymerization, thin-film polymerization, and spray polymerization, as disclosed in Japanese Kokai No. 55-133413;
saponificated copolymers of vinyl esters and unsaturated carboxylic acids or the derivatives thereof, as disclosed in Japanese Kokai Nos. 52-14689 and 52-27455;
crosslinked polyacrylic acids and salts thereof prepared by copolymerization of a monomer containing a sulfonic acid group or sulfonate group (salt of sulfonic acid group) as disclosed in Japanese Kokai Nos. 58-2312 and 61-36309; and
crosslinked copolymers of isobutylene-maleic acid anhydrides, hydrolyzates of crosslinked copolymers of starch-acrylonitrile, crosslinked carboxymethylcellulose derivatives, and crosslinked copolymers of acrylic acid or acrylate-acrylami des.
Two or more of these water absorbing resins may be used in combination. The surface-crosslinked water absorbing resins which are crosslinked on the surface with a crosslinking agent are also preferable for use in the present invention.
The salts of the monomers normally refer to a sodium salt and/or a potassium salt, but may be a salt of an organic acid such as an ammonium salt or an amine salt depending on the application of the polymerization process.
The water insoluble water absorbing resin containing a carboxylic group and a carboxylate group as the principal constituent units are most preferable since these polymers exhibit relatively larger water absorption capacity.
The water insoluble water absorbing resin containing a carboxylic group as the constituent unit have about 20-50 mole %, and preferably about 25-45 mole % of the carboxylic component based on the total number of the carboxylic and carboxylate groups. The carboxylic groups of a carboxylic component are able to adsorb ammonia.
The water absorption performance of the resin is reduced when the molar amount of the carboxylic component based on the total amount of the carboxylic and carboxylate components exceed 50 mole %. In addition, the pH of the resultant antibacterial water absorbing composition falls in the acidic range. The acidic water absorbing resin is undesirable when the resin is used in devices which contact to the skin since skin irritation usually occurs.
A carboxylic component content of less than 20 mole % results in poor ammonia adsorption. In addition, the pH of the resultant antibacterial water absorbing agent composition becomes alkaline, which also has a possibility to cause skin irritation.
The absorbency of the water absorbing resin (D) for a saline solution (an aqueous solution of 0.9% sodium chloride) is typically about 30 g/g or more, preferably 35 to 80 g/g, and more preferably 40 to 75 g/g. The absorbency is measured by using a method described below.
The shape of the water absorbing resin (D) is not particularly limited so long as it is in powdered form. The examples of suitable shapes include grainy shapes, granular shapes, agglomerated shapes, scaly shapes, lumpy shapes, pearly shapes, and impalpable powdered shapes.
The particle size distribution of the water absorbing resin (D) is also not particularly limited. Typically, the diameter of 90 wt % or more of the particles is about 1 mm or less. Preferably, the diameter of about 90 wt % or more of the particles is from about 0.1 to about 0.9 mm.
The water absorbing resin (D) and the inorganic powder mixture (C) can be mixed at a room temperature, or under heated conditions as required using standard apparatus as described above. Typically, the components are mixed for about 10 to 60 minutes. Other methods of preparation of the antibacterial water absorbing composition will become apparent to one of ordinary skill in the art.
The preparation of the antibacterial absorbing composition and mixing of the inorganic adsorbent (A) and aqueous fluid of the antibacterial agent (B) can be carried out in separate apparatuses, or in the same apparatus. Alternatively, the antibacterial absorbing composition can be line-blended in a powder transportation line during the process for producing the water absorbing resin (D).
The shape and the particle size distribution of the resulting antibacterial water absorbing composition of the present invention is not particularly limited. Suitable shapes include grainy shapes, granular shapes, agglomerate shapes, scaly shapes, lumpy shapes, pearly shapes and impalpable powdered shapes.
The particle size distribution of the resulting antibacterial water absorbing composition typically have about 90 wt % or more of the particles with a diameter of about 0.05 to 1 mm. Preferably, about 90 wt % or more of the particles have a particle diameter of about 0.1 to about 0.8 mm.
The antibacterial water absorbing composition of the present invention can be combined with other additives. Examples of suitable additives include organic powders as a bulk filler or an additive such as pulp powders, cellulose derivatives, and natural polysaccharides, inorganic powders such as calcium carbonate, bentonite, and activated carbon, antioxidants, surfactants, deodorants, coloring agents, and perfumes. The additives are usually combined with the antibacterial water absorbing composition in the amount of about 10 wt % or less based on the combined weight of the additives and the antibacterial water absorbing composition.
The antibacterial water absorbing composition of the present invention is satisfactory in both absorption and antibacterial effects when contacted with aqueous fluids. The antibacterial water absorbing composition can be used for water absorbing material in any method in which the antibacterial water absorbing composition is retained in a suitable water absorbing substrate which is used as support. The examples of the method of producing water absorbing material include scattering the antibacterial water absorbing composition between two layers of pulps or other heat fusible fibrous materials and fusing, if necessary, the layers together, mixing the antibacterial water absorbing composition with a pulp or other heat fusible fibrous materials and fusing, if necessary, the fibers together, and sandwiching the antibacterial water absorbing composition between two or more water absorbent papers, tissue paper, non-woven fibrous sheets, or fabric sheets and bonding the layers together.
The amount of the antibacterial water absorbing composition combined with the water absorbing substrate can vary depending on the kind and the size of absorbing substrate, and the desired absorbing performance. For example, in the case of disposable diapers and incontinence pads, the amount of the antibacterial water absorbent composition is typically from 3 to 25 g/piece. Alternatively, for sanitary napkins, panty liners, and nursing pads, the amount of the antibacterial water absorbent composition is typically from 0.2 to 5 g/piece. Further, when sandwiched between two or more of water absorbent papers or non-woven fabrics, the amount of the antibacterial water absorbent composition is typically from 10 to 80 g/m2.